Data was logged every second, 75,000 measurements were processed and then mapped, and now we know Northeast Washington and central Baltimore are afflicted by the most punishing heat on hot summer days.

The data was collected as part of a field campaign funded by the National Oceanic and Atmospheric Administration to better understand the urban heat island effect in the two cities. Heat islands are caused by high concentrations of asphalt and concrete, which pump up temperatures.

Specifically, the mapping project identified the following areas, cluttered with heat-absorbing surfaces, as the hottest:

In Washington: the neighborhoods of Queens Chapel, Michigan Park and Bloomingdale.

In Baltimore: the neighborhoods of Penn-Fallsway, Middle East and Milton-Montford.

The cool spots, in contrast, tended to coincide with shady, tree-lined parks. In Washington, they were Rock Creek Park and the National Arboretum, and in Baltimore, Herring Run Park and Druid Hill Park.

Map of Baltimore's heat island using data collected Aug. 29. (NOAA)

The maps not only revealed the hottest and coolest areas but also the dramatic temperature differences between some neighborhoods, often very near one another.

Temperatures varied across sections of the city by as many as 17 degrees when the field campaign was conducted in Washington on Aug. 28, one of the summer’s hottest days. Several neighborhoods saw temperatures shoot up to 102 degrees. But other locations, also within the confines of the District, merely hit 85 — a cool snap by comparison.

Many Washingtonians have long fled to the mountains or to the Atlantic beaches, driving hours at great expense, to escape Washington’s oppressive summertime heat. But this data suggests just a short walk to a well-shaded park could accomplish the same goal.

“In D.C., we were surprised by the clear boundary between green spaces and developed areas,” Vivek Shandas, a Portland State University professor who led the temperature collection effort and processed and mapped the data for NOAA, said in an email. “The National Arboretum and areas of Ivy City and Brentwood contain a difference of 10F within just a few city blocks.”

Shandas blamed the torrid conditions around Brentwood on the high concentrations of roads and buildings.

“Roads, we know from extensive research, are the hottest areas of any city, and those with adjacent large tracts of parking lots and industrial development further amplify the heat, which is what we see in these maps,” he said.

The radical temperature changes over short distances show just how important urban planning and the presence of green space can be for comfort and, during dangerously hot weather, human health and safety.

“The way that we’ve built our human landscapes amplifies heat waves, and that story is no different in D.C. and Baltimore,” said Jeremy Hoffman, of the Science Museum of Virginia, who worked with Shandas on the campaign. “This is also something we’ve done unwillingly — so we can start using this information today to design our urban areas for healthy, climate-resilient outcomes.”

Vivek Shandas from Portland State University prepares to drive through Anacostia to measure the area's heat island effect. (Jason Samenow)

Hoffman said he would like to see “community organizations, developers and government stakeholders to co-produce meaningful and equitable policies that address extreme heat disparity in D.C.”

These policies, Shandas said, would motivate officials to use these maps for targeting heat intervention programs, such as establishing cooling centers and “check on your neighbor” initiatives in the most vulnerable areas.

Policies could also be developed to support efforts to alter the environment in the hottest areas by introducing green space and changing building materials and design practices. Studies have shown these efforts can lower temperatures.

“We know that climate change is going to bring more dangerously hot days, and these maps show which neighborhoods are going to be most impacted,” said Kate Johnson, chief of the green building and climate branch in the District’s Department of Energy and Environment. “The maps also show us that we can keep neighborhoods cooler by making them greener. The Bowser administration is already investing in planting trees and replacing our paved surfaces with green space that can help capture rainwater while keeping us cool.”

Shandas hopes the campaign data and subsequent analysis can bolster the District’s efforts.

“The logical next step in this campaign is to assess what changes in the environmental, land use and material characteristics can help lower temps,” Shandas said.

Jason SamenowJason Samenow is The Washington Post’s weather editor and Capital Weather Gang's chief meteorologist. He earned a master's degree in atmospheric science and spent 10 years as a climate change science analyst for the U.S. government. He holds the Digital Seal of Approval from the National Weather Association. Follow